The present invention relates to electrical power distribution systems and more particularly to apparatus for protecting electrical power distribution lines and equipment.
Protection of power lines and power line distribution equipment is key to providing constant service to all utility customers. In order to have a safe reliable system of power distribution, protective relaying is utilized. To prevent permanent costly damage from occurring to the distribution networks of the utilities, the protective relaying system must be able to clear short-term faults and isolate the protected zone during phase-to-ground and three phase faults quickly and reliably. One method of providing this protection is pilot wire relay protection.
Pilot wire relay protection typically utilizes two electro-mechanical relays, one at each end of a protected zone, and a communication channel connecting these relays. Typically, the communication channel is a dedicated telephone line provided by the telephone company. The power companies either lease or purchase these dedicated telephone lines. The dedicated telephone line, which in the past consisted of wires, is the path that the two relays use to communicate. This proved to be very effective in performing pilot wire relay type protection of electrical power distribution lines because the hard wired telephone communication channels allowed for simple current flow across the pilot wire which would close the relays and trip the associated circuit breakers thereby isolating the fault in the electrical power distribution system.
However, with the perfection of the fibre optic communication channels, the telephone companies have been upgrading their systems by replacing hard wired telephone communication lines with the fibre optic communication channels. Such upgrading presents problems for the power companies which utilize pilot wire relay protection. With the installation of the fibre optic communication channel, there is no longer a wire communication channel over which the current can flow. In addition, the fibre optic communication channels being used by telephone companies have a limited bandwidth, in the audio band of approximately 300 to 3200 Hz. The signals which typical pilot wire relays produce occur at 60 Hz. Since such signals are below the lower limit of the bandwidth of the fibre optic communication channel, they will not be transmitted across a communication channel of this type.
It is therefore an object of the present invention to provide an apparatus which will enable pilot wire relay devices to communicate across a fibre optic communication channel.
It is another object of the present invention to provide an apparatus for enabling existing pilot wire relay devices to communicate across the fibre optic communication channel without replacing such pilot wire relay devices.
It is still another object of the present invention to provide an apparatus for enabling existing pilot wire relay type devices to communicate across fibre optic communication channels without the need for internal modifications to the existing pilot wire relay devices,
These and other objects of the present invention will become apparent to those skilled in the art upon consideration of the following description of the invention,